Separation of aromatic acids



June 24, 1958 G. c. FE'IGHNER r-:rAL 2,840,604

SEPARATION 0F AROMATIC ACDS Filedr May 2, 1955 SELECTIVITY vOF-'METHANOL AS A SOLVENT FOR PHTHALIC ACID 5 C .5 nu 5 AU 5 3 3 2 2 l TEMPERATURE a! ZW/ZJ' @TTORNEY 2,840,604 SEPARATION OF AROMATIC ACIDS George C. Feghner and Adolph C. Shotts, Ponca City,

Okla., assgnors to Continental Oil Company, Ponca City, Okla., a corporation of. Delaware Appuafion May z, 195s, serial No. 505,359 s claims. (cino- 525) This invention relates to; a process for separating a mix-ture of benzene dicarboxylic acids and benzoic acidsV into its components. More particularly this invention provides amethod of separating parab'enzene dicarboxylic acid, commonly called terephthalic acid, from benzoic acid and metabenzene-dicarboxylicacid, commonly called isophthalic acid.

The separation of a mixture of benzene dicarboxylic acids into meta and para isomers is troublesome. The orthoisomer is readily separated from `the `meta and para isomers since'the ortho isomer alone forms an anhydride. The usual physical and chemical means of separation, however, are not `effective for separating isophthalic from `terephthalic acid' because of their similar properties.

precipitates therefrom and is separated from the reaction.

mixture by filtration. Such la method `is effective for separating these two acids, howeverfif isophthalic acid is the desired product, the ester, of course, must'be saponified.

Accordingly it is an object of this inventionto provide a process for separating mixtures of terephthalic acid, isophthalic acid and benzoic acid from a mixture thereof, which method obviates the disadvantages of the prior art processes. Another object offour invention is toprovide a method for the separat-ion of these Vacids whichdoes not involve esteriication. It is yet another object of the present invention to provide a method-for the separation of terephthalic acid, isophthalic acid and benzoic .acid from the products of oxidation of a mixture of paraxylene, methaxylene and ethylbenzene. Other objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description.

In brief, the foregoing objects and advantages are obtained by a process which comprises the extraction of a mixture of terephthalic, isophthalic and benzoic acids with a selective solvent in which the terephthalic acid is relatively insoluble and in which benzoic acid is more soluble than is isophthalic acid. Extracting the mixture of the three acids with such a solvent willdissolve the isophthalic and benzoic acids. After separating the dissolved acids from the insoluble terephthalic acids the isophthalic acid may be recovered from the solution of benzoic and isophthalic acids by evaporating a portion of the selective solvent. Since the isophthalic acid is not very soluble in the selective solvent, the isophthalic acid will precipitate ,out when very much of the solvent has been evaporated.

United States Patent() The isophthalic acid can be separatedv from the benzoic acid by filtration. Y

Somewhat more specifically the present invention provides a method by which relatively pure terephthalic, isophthalic and benzoic acids may be recovered from the oxidation products of paraxylene, metaxylene and ethyl benzene. Generally such mixtures will contain from about .l to .5 part of benzoic acid and from l lto 3.5 parts of isophthalic acid per part of terephthalic acid. A suitable amount of the selective solvent may vary from about 35 to 350 parts per part of isophthalic acid. Quantities of solvent in excess of 350 parts may be used but no particular advantage is attained thereby. Suitable solvents are stable inert volatile organic liquids having a dissolving power for the isophthalic acid which is about 10 tor times as great as for terephthalie acid. Specific solvents include the'l'ower 'aliphatic alcohols, ketones and carboxylic acids, as for example, methanol, ethanol, normal propanol, isopropanol, tertiary butanol, acetone,`

methyl ethyl ketone, diethyl ketone,Y methyl isobutyl ketone, formic acid and dioxane and tetrahydrofurane. Mixtures of two or more of the above-named solvents may be used also. 4 Alternatively and somewhat preferably the initial extraction is carried out with one solvent and the final extraction with a second solvent. As for example, benpzoic acid may be extracted from the, mixture of the three acidsrbyusingas a solvent benzene acetic acid ori toluene which will dissolve outthe benzoic acid and not extract either of 'the phthalic acid isomers.v The ter'ephthalicy and isophthalic acid may then 'be' separated by extracting the extrahendwith. methanol ory ethanol preferably at a temperatureof about 2'0-254" C. .Temperatures higher' than 20 to 25 C. may beused with van overall reduction in the quantity of solvent required. Such a result is accomplished, however, at a sacrifice in selectivity'of the solvent for' the two phthalic acids, hence our preferred temperature range. That is, the higher the temperature, 50 C. and above, the less solvent'required but the separation Aofjthel two acids willnot be as sharp and each ofthe acidsso recoveredy willl contain'a greater l quantity offthe other acid than if the extraction were conducted ratthe lower temperature. This resultisy apparent from theaccompanying drawingv wherein' the selectivity of methanol for the two acids is plotted versus temperature. Similar curves were obtained using the other aliphatic alcohols, ketones and carboxylic acids listed above.'

In order to disclose thenature of the present invention still more clearly, the following illustrative examples will be given. notto be limited tothe'specific conditions orr details set forth in these examples except insofar as such limitations are specified .in the appended claims. In the examples, .parts given are parts by weight.

Example 1 A reactor was charged with 2O parts of a refinery stream analyzing 18.6% ethylbenzene, 65.3% m-xylene and 16.2% p-xylene, 250 parts of water, and 5 parts of po' tassium hydroxide. While the mixture was being agitated and heated to reflux (93-95 C.) there was added over a period of 3 hours 110 parts of potassium permanganate. Following the addition of the permanganate the mixture was heated at reflux for an additional hour. After acidifying the mixture, 5.7 parts of unreacted hydrocarbon and 18.6 parts of solid acids analyzing 63% isophthalic acid, 35% terephthalic acid and 2% benzoic acid were recovered; the latter recovered from the aqueous phase.

Example 2 The acid mixture obtained in Example 1 was treated,y

with 760 parts of ethanol at 20 C. On filtering there was It is to be understood that the invention is parts of isophthalic acid containing about 3% terephthalic acid., Concentration ofthe filtrate `yiel ded.0.5 part` of `impure benzoic acid.`

i Example 3 second extrahend of about 5 parts of relatively pure isophthalic acid was'ob- Tenparts of a mixture of acids containing 59.2%.isophthalic acid, 30.2% terephthalic acid and` 10.6% benzoic acid was extractedwith tive 65 part portions of methanol `at 25 C. The extrahend consisted of 3 parts of `pure terephthalic acid. The extract was distilled to concentrate the remaining acids and recover methanol. When a thick slurry wasobtained in the still pot, the material was, cooled andpressA filtered. There was obtained 5.9 parts ,of isophthalic `acid analyzing `96.7% isophthalic acid. Concentration of the ltrate yielded about 1 part of a mixture of acdslthat was primarily benzoic.

Example 4 Ten parts of the acid mixture used in Example 3 was wet `with 3.5 parts of methanol. The' mixture was gave about lk part of crude benzoic acid. The extrahend was extracted with tive v65 part portions of methanol at 25 C. On concentration of the combined extracts about 6 parts of isophthalic acid was obtained. The remaining extrahend consisted of almost pure terephthalic acid.

r Example5 Ten parts of an acid mixture as usedin Example 3 was extracted with three 200 part portions and then three 100 i press tltered yielding an extract which on concentration part portions of acetone` at 25 C. `The extrahend consisted of about 3 parts of terephthalic acid. Theextract was distilled to concentratethe remaining acids. From the concentrate in the still was obtained 6.0 parts of isophthalic acid by.filtra`tion. 0n evaporation of the filtrate a mixture of acids that was primarily benzoic-v was obtained.

.i i Example 6 I Tenparts of an acid mixture such as used in Example 3 was extractedwith three porh'ons of 10 parts each of benzene. The combined extracts lyielded about -1 part of relatively. pure benzoic acid.` Theextrahend was then extractedwith live 65 part portions of methanol.l On concentration of the combined extracts4 about 5.9 parts of relatively pure isophthalic acid was obtained. The second extrahend consistedV of almost pure 'terephthalic acid. t t.

tained.. From the ltrate 2.8 parts of' a mixture of acids primarily benzoic 'and toluic acids was obtained.

While particular embodiments of the invention have been described, it will beunderfstood, of course, that the invention is not limited thereto since many modifications may be made, and it is, therefore, contemplated to cover by the appended claims any such modifications as fall within the true spirit and scope of the invention.

The invention having thus been described, what is claimed and desired to be secured by Letters Patent is:

1. A process for the separation of amixture of aromatic acids comprising per part of terephthalic acid in said mixture, 1 to 3.5 parts isophthalic acid, and .1 to .5 part benzoic acid, which comprises removing the benzoic acid from said mixture by extracting said mixture with about 3 parts acetic acid per partof said acid' mixture, to form an extract comprising benzoic acid dissolved in said acetic acid, and an extrahend comprising isophthalic acid and terephthalic acid, then extracting the extrahend with about 35 to 350 parts of a solvent per part ofsaid isophthalic acid selected `from, the group consisting` of aliphatic alcohols having from 1 to 5 carbon. atoms and ketones having from 3 to 5 carbon atoms, per part of isophthalic acid to form an. extrahend comprising relatively pure terephthalic acid and an extract comprising isophthalic acid dissolved in said solvent, both extractions being carried out at a temperature of from 20 to 25 C., then concentrating the extracts, and filtering said concentrated extracts to remove the isophthalic acid, and benzoic acid from their respective solvents.

2. The process of claim 1 wherein the benzoic acid. is extracted with about 3 to 10 parts of acetic acid per part of isophthalic acid in the mixture. j

3. The process of claim 1 wherein the second mentioned solvent is acetone.

4. The process of claim 1 wherein the second meutioned solvent is methanol.

5. The process of claim 1 wherein the second men tioned solvent is ethanol.

References Cited in the tile of thispatent. UNITED sTATEs PATENTS t 2,741,633 Mcxinnis et al. .`-.apr'} 1o, i936 FOREIGN PATENTS A y v if 329,375 Great Britain y May 19, i930 OTHER REFERENCES Fittig et al.: Liebigs Ann., vol. 148, pp. 11-23 (1868)'. Bonz: Ber. Deut. Chem., vol. 18, p. 2305 (1885). Ullman et al.: Ber. Deut. Chem., vol. 36, p.1798 1903). 1

McMaster: Am. Chem. J., vol. 49, 298 (1913). Heilbron: Dictionary of Organic Compounds, vol. 1, p. 255, vol. III, p. 104, and vol. IV,^p. 404 (1953). 

1. A PROCESS FOR THE SEPARATION OF A MIXTURE OF AROMATIC ACIDS COMPRISING PER PART OF TEREPHATHALIC ACID IN SAID MIXTURE, 1 TO 3.5 PARTS ISOPHTHALIC ACID, AND .1 TO .5 PART BENZOIC ACID, WHICH COMPRISES REMOVING THE BENZOIC ACID FROM SAID MIXTURE BY EXTRACTING SAID MIXTURE WITH ABOUT 3 PARTS ACETIC ACID PER PART OF SAID ACID MIXTURE, TO FORM AN EXTRACT COMPRISING BENZOIC ACID DISSOLVED IN SAID ACETIC ACID, AND AN EXTRAHEND COMPRISING ISOPHTHALIC ACID AND TEREPHTHALIC ACID, THEN EXTRACTING THE EXTRAHEND WITH ABOUT 35 TO 350 PARTS OF A SOLVENT PER PART OF SAID ISOPHTHALIC ACID SELECTED FROM THE GROUP CONSISTING OF ALIPHATIC ALCOHOLS HAVING FROM 1 TO 5 CARBON ATOMS AND KETONES HAVING FROM 3 TO 5 CARBON ATOMS, PER PART OF ISOPHTHALIC ACID TO FORM AN EXTRAHEND COMPRISING RELATIVELY PURE TEREPHTHALIC ACID AND AN EXTRACT COMPRISING ISOPHTHALIC ACID DISSOLVED IN SAID SOLVENT, BOTH EXTRACTIONS BEING CARRIED OUT AT A TEMPERATURE OF FROM 20 TO 25*C., THEN CONCENTRATING THE EXTRACTS, AND FILTERING SAID CONCENTRATED EXTRACTS TO REMOVE THE ISOPHTHALIC ACID, AND BENZOIC ACID FROM THEIR RESPECTIVE SOLVENTS. 